Another occasion is the successful release of "In the Shadow of the Moon," a documentary that retells the story of America's space effort, using the voices of the astronauts themselves. One of those astronauts is Apollo 17's Harrison Schmitt, whose name is the very last on a chronological list of humans who have walked on the moon. After his stint at NASA, Schmitt went on to become a one-term Republican senator representing New Mexico. Today, at the age of 72, he serves as chairman of the NASA Advisory Council.

Schmitt cautions that it's going to take more than a movie - or a golden anniversary - to push the world into a new Space Age.

"It's going to come from circumstances, and a more general understanding of just how important space is in the future of humankind," he told me. "Unfortunately, our educational system is not teaching history, much less providing the kind of information to the general electorate that is necessary to understand why space and other major projects ... are important to the future of the country, and the future of humankind."

OK, so what are the whys and wherefores for the next 50 years? Here are five E's that come to mind, in roughly chronological order if not in order of importance:

1. ExplorationThis is NASA's oft-stated reason for heading back to the moon and setting its sights on Mars and beyond. Even though the first space race was primarily a clash of empires (see No. 4 below), Schmitt said the space effort's scientific and technological benefits are still underappreciated, 35 years after the last moon mission.

The trips to the moon marked the first time humans ever explored a "second planet," and studying the lunar surface shed light on Earth's hidden origins as well, Schmitt said. "To have that contextual information about what the nature of the environment was here on Earth, during the first almost billion years of Earth history ... is extremely important scientifically, and philosophically as well," he said.

But is exploration alone enough of a reason to spend tens of billions, even hundreds of billions of dollars on spaceflight? To sustain that outward push, and justify the risks to humans, weightier reasons are needed.

2. EntertainmentEntertainment may not sound like a weighty reason for expanding the space age. But it already has a proven economic payoff. And you don't even have to go into space. Even our "Space Shots" slide show is an example of space-themed entertainment with financial benefits (in the form of ad revenue). Space camps, tourist destinations and zero-gravity airplane flights are other examples of earthbound entertainment with space themes. To celebrate the Sputnik anniversary, nine students from around the world will be taking a zero-gravity flight from Las Vegas on Saturday, thanks to the sponsors of World Space Week.

Even Schmitt has space-based entertainment on his mind. For years, he's been working with retired professor Ron Wells on the concept for a virtual-reality simulation of lunar landing sites. Players would put on VR headsets and walk around a modeled moonscape, seeing high-resolution lunar vistas in a 3-D setting.

In a series of e-mails, Wells told me that he's looking into the financial as well as the technical aspects of the project. The plans could heat up after next year's scheduled launch of NASA's Lunar Reconnaissance Orbiter.

"A major inroad to really seeing what the moon looks like as the astronauts themselves saw it will occur when the Lunar Reconnaissance Orbiter starts sending back extremely high resolution images of the lunar surface," Wells said. "I hope to be in a position by that time to be able to do something more than just talk about it."

Schmitt said the project could take on a more serious purpose in the years ahead.

"It will provide not only that opportunity for the public to visit at least the last three mission landing sites ... but it also is going to be something that will be very useful, I think, in training future explorers of the moon as well as future settlers of the moon."

Meanwhile, on the high end of the entertainment spectrum, five people have paid up to $25 million each to buy Russian rides to the international space station. A sixth "private space explorer" (also known as space tourist) made himself known just last week. Virginia-based Space Adventures brokered all those trips - and the company's president and chief executive officer, Eric Anderson, told me that many more such trips could be on the way.

"Within five years' time we could be signing up 10 people per year on orbital flights," he said today.

Anderson said his company has proved that private enterprise can make space travel profitable.

"We've created a new market," he said. "People before Dennis Tito's flight did not believe that someone would pay $20 million, let alone $30 million or $40 million, to go to orbit. ... I think that the work that we've done here on the eve of the next 50 years in space will certainly be a huge motivator."

Space Adventures' next giant leap would be a $100 million-per-seat tour around the moon, which the company is offering in cooperation with the Russian space agency. "I love that mission, but I'm still working on it," Anderson told me. "We're just going to have to see."

3. EnergyIf there's ever going to be a space gold rush, it will take more than entertainment. After all, Christopher Columbus didn't sail to America 500 years ago just to take passengers on tours of the ocean blue. He was looking for trade advantages, and riches as well.

Anderson expects that the payoffs from space exploration will become more attractive in the decades ahead. "In 100 years or more, or even sooner, space will be far more critical to our welfare on Earth even than it is now," he said. "Being able to use the resources in space, and perfect transportation systems that can take us to space, is something we have to do."

When Anderson talks about resources in space, he's not necessarily talking about shipping space rocks back to Earth. Sure, some folks may put their faith in asteroid mining, but the bigger prize would be cheaper energy from space.

Schmitt has another energy strategy in mind: extracting helium-3 from lunar soil and transporting it to Earth for use in future fusion reactors. Helium-3 is a substance that's rare on Earth but much more abundant on the moon, and Schmitt argues that it would make an environmentally clean, economically affordable fuel once the fusion process is perfected.

"The economics are competitive with the current price of coal, and as energy prices go up, they just become increasingly competitive with those other energy sources that we use today on Earth," he said.

Commercial fusion power may sound as much like science fiction as affordable moon travel, but Schmitt insists that researchers at the University of Wisconsin at Madison and elsewhere are making progress toward a workable reactor that would use helium-3.

"It's not pie in the sky," Schmitt told me. "These things are happening. Of course, break-even is a long way away, but it still is something that has gone forward with very, very little funding."

Would it still be worth the risk and expense to ferry helium-3 from the moon to Earth? If the fusion dream really does come to pass, and if the ore extraction and delivery could be done robotically, Schmitt's calculations could conceivably make sense. For more on the concept, you can delve into his book, "Return to the Moon."

4. Empire buildingWhen enthusiasts gush about moon tours, space solar power and fusion fuel, it's sometimes easy to forget that we already have a huge economic stake in keeping the peace on Earth's satellite frontier. Over the past 50 years, satellites have revolutionized daily life - and if further space exploitation can yield even higher returns, that just raises the stakes for defending against an orbital "Pearl Harbor" attack.

This January, China sparked a mini-Sputnik spat when it fired a rocket to shoot down one of its own satellites. Other countries feared that such test shots could eventually open the way to space warfare - although Chinese officials said that wasn't their intent. Nevertheless, the old concerns about national competitiveness have been reawakened by recent developments, including NASA Administrator Michael Griffin's view that Chinese astronauts could well set foot on the moon before American astronauts return there.

"For the United States to sit back and let other nations move forward in this arena would be extraordinarily detrimental to our self-esteem, as well as to our ability to compete in other arenas on this planet," Schmitt said. "Whether we think we have a choice or not, we do not - particularly with respect to China."

Of course, the world has changed since Sputnik in 1957 and Apollo in 1969. Washington and Moscow aren't the only ones with space programs anymore - and NASA can no longer presume to speak "for all mankind."

To keep the peace, Russia, China, Japan, India, Europe and other space players will have to have a piece of the action. Just this week, the Secure World Foundation issued a call for a global space action plan, complete with an international space traffic management system and cooperative space surveillance system.

Some parts of the plan may sound too utopian, but an international approach to managing satellites, orbital debris and potential threats from near-Earth objects is already taking shape. After all, in the long run, we're all in this together.

5. Extinction avoidanceIn the long run, we're all dead. But we still hope that civilization will endure even after our own bodies have turned back into stardust. Underlying the next phase of the space age is the idea that the human species will have to extend itself outward to new frontiers, if it is to survive a future cataclysm like the asteroid strike that killed off the dinosaurs 65 million years ago.

Sure, the chances of a civilization-killer - or even a "cosmic Katrina" caused by a smaller space rock - are astronomically low. But now is as good a time as any to start the outward push, Space Adventures' Anderson said.

"All of this is something that is very long term, but of critical need to humanity," he told me. "Commercial human spaceflight is a small part. Maybe it's not such a small part. Maybe it's a big part."

Feel free to weigh in with your own thoughts on the next space age, and have a great Columbus Day weekend. The next Cosmic Log posting will be on Monday.